1. Field of the Invention
The present invention concerns an improved friction device for a clutch, in particular for a motor vehicle.
2. Description of the Related Art
A motor vehicle clutch is intended to transmit a torque between an engine flywheel of the motor vehicle and a gearbox input shaft. For this purpose, the clutch comprises a mechanism rotationally fixed to the engine flywheel and a friction device rotationally fixed to the gearbox shaft.
The mechanism comprises a pressure plate and a reaction plate, intended to cooperate with first and second friction linings of the friction device. These friction linings are carried by at least one support, normally generally of revolution in shape.
The friction device must achieve a compromise between various technical constraints.
On the one hand, it is necessary to limit the mass and inertia of the friction device.
For this purpose, it is wished to limit the dimensions of the friction linings, for example the thickness and radial width of these friction linings. It is also wished to avoid the presence of rivets fixing the linings to their support by opting as far as possible for the adhesive bonding of these linings to their support.
On the other hand, it is necessary to be able to actuate the clutch progressively.
For this purpose, it is wished to incorporate elastic means, in general an elastomer mass, in the friction device, in order to ensure this progressiveness.
Shearing effects limit the possibilities of arranging the elastomer mass between a lining and its support.
There has therefore been proposed in the prior art, in particular in EP-A-0 419 329, a friction device for a clutch, in particular for a motor vehicle, of the type comprising first and second friction lining members, substantially annular and coaxial, separated axially and delimited by opposing friction faces.
In a friction device of this type, the friction lining members each comprise a support carrying a friction lining. In this case, the elastomer mass is interposed between the first and second supports.
More particularly, each lining support described in EP-A-0 419 329 comprises a peripheral part annular in shape overall and a central part for connection with the other lining support. The central parts of the supports are contiguous. The peripheral parts of the supports, separated axially from each other, are connected to the central parts by intermediate parts converging from these peripheral parts towards these central parts.
Because of this, when the friction linings are clamped between the pressure and reaction plates, the peripheral parts of the lining supports deform, diverging towards the intermediate parts of the axially relatively rigid supports. Consequently the separation between the peripheral parts of the lining supports does not vary uniformly radially, when the friction linings are clamped between the pressure and reaction plates.
As a result the friction linings do not cooperate uniformly radially with the pressure and reaction plates, which impairs the performance of the clutch.